The invention relates to a gas-cooled high temperature reactor installed in the cavity of a prestressed cylindrical pressure vessel. More particularly, the invention is directed to gas-cooled high temperature reactors with supporting structure having gas conduits therein. Generally, a hot gas collector space is located underneath the supporting structure and a plurality of radial hot gas conduits connect with the hot gas collecting space, wherein the core structure of the high temperature reactor is surrounded by a lateral thermal shield and the supporting structure rests on a floor plate by means of columns arranged in the hot gas collecting space.
Supporting structures for a moderator block consisting of vertical moderator columns of a gas-cooled nuclear reactor are known. In these structures, a plurality of supporting plates are arranged in a plane adjacent to one another but with lateral clearance. Each supporting plate carries a limited number of the moderator plates. Such a supporting structure is described, for example, in West German Published Application 11 77 751. Each supporting plate rests on a solid support by means of three pillars, with the support in turn resting on the floor of the reactor vessel. The pillars, in the form of round columns, have a central part of steel, a sheathing and a thermal insulating layer between the central part and sheathing.
West German Published Application 11 22 641 shows a supporting structure for the moderator of a nuclear reactor wherein each of the vertical columns forming the moderator structure are carried by a rigid metal cylinder. The moderator columns and the metal cylinders support each other by way of a spherical support surface in the manner of a ball and socket joint. Each metal cylinder is equipped at its foot with a circular collar resting on a seat machined in a socket. The socket is part of the supporting structure, the lines for the cooling medium enter it from below.
It is known from West German Published Application 11 94 071 to support the moderator structure consisting of solid material of a nuclear reactor on a flat supporting suface. The surface is composed of several rigid supporting surface parts. Each part of the supporting surface is carried by a plurality of supporting posts provided individually with an articulated joint at their end in the vicinity of the end connected with the flat supporting surface. The lower ends of the supporting posts are rigidly secured in supporting stirrups, which in turn are resting on the floor of the reactor cavity.
Another supporting structure for the core of a gas-cooled nuclear reactor is described in West German Offenlegungsschrift No. 19 56 226. The core is supported on the floor of the reactor pressure vessel by means of a refractory material. In an upper layer of the refractory material voids are formed for the cooling gas. The voids are interconnected with each other and with the cooling gas conduits in the core structure. The voids also serve as the collector space with gas being conducted through a laterally connected hot gas conduit from the reactor.
The upper layer of the refractory material rests upon a lower layer formed by supporting columns resting on the floor of the pressure vessel, wherein each supporting column has a spherical seat, for example, of steel or cast iron.
The state of the art further includes a supporting floor for a pebble bed reactor (a reactor known as THTR300 MWe), consisting of a plurality of hexagonal graphite blocks arranged into freely movable columns. Each of these colums is provided with a plurality of radial bores for receiving the cooling gas flowing from top to bottom through the pebble bed. Each of the columns is supported individually by a massive round column. All of the round columns are secured into the floor of the nuclear reactor, which consists of graphite plates. The hot cooling gas exiting from the supporting floor passes into the columnar hall formed by the round column. The hall serves as the hot gas collector space and is connected with several radial hot gas conduits. The radial hot gas conduits conduct the hot gas to the steam generators.
A further supporting structure, preferably for the core of a gas-cooled high temperature reactor with spherical fuel elements, is known from West German Offenlegungsschrift No. 27 18 493. Here again, the supporting structure consists of a plurality of graphite blocks arranged in layers above each other and provided with passages for the cooling gas. The bottom layer is formed by a plurality of support units composed of individual segments and each of the support units rests by means of a column head on a round column. The round columns pass through the hot gas collector space and are bonded into the floor of the nuclear reactor.
In West German Offenlegungsschrift No. 26 36 251 a floor for a large vessel exposed to high and varying temperatures and consisting of numerous elements of a material resistant to high temperatures is described. The elements, maintained together by an external support, are bearingly supported on roller bodies, the rolling planes of which are inclined downwards with respect to the support and/or a fixed point.
There is further known a yielding support for the heavy components of thermal power stations, such as for example, reactor pressure vessels or steam generators. The yielding support consists of a plurality of compressively stressed support rods. The yielding property of the support is accomplished by arranging several identical support rods adjacently to each other in the direction of the yielding. This support is described in West German Offenlegungsschrift No. 26 20 584.
All of the above-described structures constitute the background and starting point of the present invention. Gas-cooled reactors of the high temperature design for the nuclear reactors of this invention have floor plates upon which the supporting structure of the nuclear reactor is resting. These floor plates must satisfy requirements of very different natures. Firstly, the lifting of the core structure as the result of the sudden onset of high transient pressure in the hot gas collector space (due to a failure in the cooling gas circuit) must be prevented. This requires a solid connection of the floor plate with the bottom of the cavity, i.e. the bottom of the pressure vessel. Secondly, in the operating state of the high temperature reactor, thermal expansion occurs in the floor plate and the pressure vessel to a different degree as the result of different temperature exposures. Compensation for this is required to avoid the generation of thermal stresses between the two components.